The invention relates to the field of detergency and in particular to biodegradable detergent compositions. It discloses more particularly biodegradable polymers comprising polyacrylate-based branches.
Generally, detergent compositions involve a number of chemicals. These must be biodegradable in order not to be harmful to the environment. Conventionally, detergent compositions and cleaning agents include phosphates. The latter are very efficient and relatively nontoxic; however, they lead to the eutrophication of natural aquatic environments.
Phosphates have been partially replaced in formulations for detergency by polymers, such as poly(acrylic acid)s or copolymers based on acrylic acid and on maleic anhydride.
Although the polyacrylates currently used do not present this problem, their absence of rapid biodegradability leads to an accumulation in the natural environment (Swift, Polymer Degradation and Stability, 45, 215-231, 1994).
Toxicity associated a priori with these polymers is not known but their long-term effect is uncertain and this uncertainty has contributed to the initiation of numerous research studies intended to improve their biodegradability.
It is clearly established that hydrophilic polymers, such as poly(vinyl alcohol), are rapidly degraded by microorganisms (Macromol. Chem. Phys., 196, 3437, 1995). It is also known that poly(acrylic acid)s with a weight-average mass of less than 1 000 exhibit better biodegradability than their higher homologs (Swift, Ecological Assessment of Polymer, 15, 291-306, 1997).
EP 0 497 611 discloses the preparation of biodegradable terpolymers and of the compositions comprising them. These terpolymers are based on vinyl acetate, acrylic acid and maleic anhydride. They exhibit weight-average masses of less than 20 000.
U.S. Pat. No. 5,318,719 discloses a novel class of biodegradable materials based on the grafting of polymers comprising acid functional groups to a polyoxyalkylene-based biodegradable support.
Other studies indicate that chains comprising heteroatoms are more easily degraded than carbonaceous chains. Thus, U.S. Pat. No. 4,923,941 discloses biodegradable copolymers comprising carboxylic acid functional groups and heterocycles, and the detergent compositions comprising them.
The Applicant Company has now found an effective solution for the preparation of biodegradable polymers for detergency.
These biodegradable polymers, constituting one of the subject matters of the invention, are composed of hydrophilic acrylic polymers carrying carboxyl functional groups, the structure of which is characterized by a biodegradable core (A) to which are attached at least two polycarboxylic chains (B) via bonds (C) degradable by hydrolysis or by oxidative cleavage. These polymers are also characterized in that each polycarboxylic chain has a degree of polymerization which confers good biodegradability on it and which confers, on the combination, good functional properties with respect to the detergent composition.
These structures thus play their role of builder throughout a detergency cycle but, because of the high pH of the detergent medium, gradually undergo alkaline hydrolysis of their hydrolyzable functional groups (C), which releases the acrylic polymers (B). The optionally unhydrolyzed residual part will undergo, in a second step, enzymatic hydrolysis by bacterial proteases or esterases active in the natural environment. Finally, only the core, which is readily biodegradable, and the polymers (B), the low molecular mass of which will allow rapid degradability, will remain.
The polymers of the invention correspond to the following general structure:
Core (A)-[-cleavable bond (C)-X-hydrophilic acrylic polymer (B)]n
in which n is an integer between 2 and 10 and X is a bivalent atom, such as sulfur.
The core A according to the invention is generally a branched biodegradable molecule or a biodegradable molecule which can give rise to at least two branchings chosen from the group comprising pentaerythritol, trimethylolpropane and ethylene glycol. The polymer B is either a poly(acrylic acid) or a polymer comprising acrylic acid and at least one monomer chosen from the group comprising: unsaturated carboxylic monomers other than acrylic acid, maleic anhydride, vinyl or acrylic monomers, or diene monomers, such as isoprene or butadiene.
B generally has a weight-average mass of between 100 and 2 000.
The functional group C bonding the polymer B to the biodegradable core is a labile bond hydrolyzable by the alkaline or enzymatic route, such as an ester, amide, thioester or thioamide bond, or cleavable by chemical or biological oxidation, such as a double or triple bond.
The biodegradable polymers of the invention can be prepared in various ways. They are advantageously prepared in the following way:
In a first step, the B-X block is prepared, taking care to terminate it with a reactive functional group, by radical polymerization of the monomer(s) in the presence of a reactive transfer agent, in this instance a mercaptan. Subsequently, the functionalized block is reacted with the core A. The respective amounts of A and B are defined so as to have the number of desired branches.
Another alternative form of synthesis consists, in a first step, in modifying the core, so as to prepare:
Core (A)-(-C-X)n
and subsequently in polymerizing the monomer(s), so as to directly form the polymer B on the biodegradable core.
The examples described later fully illustrate the method of preparation of the biodegradable polymers of the invention.
The biodegradability of the polymers prepared is evaluated in the following way:
The level of degradation obtained is evaluated by liquid chromatography under the following conditions:
Column: TSK 3000 Tosohaas
Calibration of the column is carried out by virtue of polyacrylate standards (Polymer Laboratories).
The degradability of the polymer under the conditions of the test is measured by the shift in the peak observed by liquid chromatography toward lower molecular masses.
This shift is quantified through a degradability index I1000 defined in the following way:
1xe2x80x94Alkaline Degradation
The sample of polymer is dissolved in a 0.08M borate buffer, pH 12, in a proportion of 10 mg of polymer per 10 ml of buffer solution. Each trial is subsequently stirred magnetically for a predetermined time in a bath thermostatically controlled at the desired temperature.
Analysis is carried out by liquid chromatography (see above) directly on a withdrawn sample of the reaction mixture after neutralization with 0.1M HCl, in a proportion of 1 ml of HCl per 1 ml of withdrawn sample.
2xe2x80x94Microbiological Degradation
Respiration Test: Warburg Method
The respiration of C. tropicalis on a polyacrylate is evaluated in Warburg flasks (total capacity 3 ml) comprising 1.3 ml of 0.1M phosphate buffer, pH 6, 1 ml of yeast suspension (approximately 3 mg dry weight) and 0.5 ml of 1.12 g.lxe2x88x921 polyacrylate (final concentration of 200 ppm).
Control tests are carried out in parallel:
a flask comprising only phosphate buffer (2.8 ml) makes it possible to measure the variations in atmospheric pressure,
the endogenous respiration is measured in a flask comprising only phosphate buffer (1.8 ml) and the yeast suspension (1 ml),
the respiration due to contaminants possibly present in the acrylate solution is also evaluated by a test comprising the acrylate (0.5 ml) and the phosphate buffer (2.3 ml),
the flasks are agitated in a water bath at 30xc2x0 C.,
the measurements of variation in pressure due to the appearance of CO2, which reveals metabolism of the acrylate by the yeast, are made every 15 minutes.
Assimilation Test: Cultures of Complex Flora on Polyacrylate
These cultures are employed on a conventional mineral medium (MgSO4.7H2O 3 g; CaCl2.2H2O 0.1 g; NaCl 1 g; FeSO4.7H2O 0.1 g; ZnSO4.7H2O 0.1 g; CoCl2 0.1 g; CuSO4.5H2O 10 mg; AlK(SO4)2.12H2O 10 mg; H3BO3 10 mg; Na2MoO4.2H2O 2 mg; q.s. for 1 liter of distilled water) in combination with 0.1M phosphate buffer, pH 7, in the proportions 2/98. The polyacrylate tested is at a final concentration of 500 ppm.
The treatment plant sludges are diluted to a third in 0.1M phosphate buffer, pH 7, with 100 mg.lxe2x88x921 of sample of polyacrylate to be tested, and then the culture is subcultured on a medium comprising 500 mg.lxe2x88x921 of polyacrylate to be tested. The flasks are incubated at 30xc2x0 C. in Monod tubes with transverse agitation and are subcultured after one week. The culturings are then continued for 30 days under the same conditions. Treatment plant at Trets, Var, France.
3xe2x80x94Evaluation of the Ability to Complex Calcium
The principle of this test consists in measuring the ability of a given polymer to prevent the formation of a CaSO4 precipitate from sodium sulfate and calcium chloride.